The present disclosure relates to exhaust gas-driven turbochargers having a variable-geometry member for regulating the flow of exhaust gas through the turbine. The disclosure relates in particular to a linear actuator for effecting movement of the variable-geometry member.
Turbochargers for internal combustion engines often include some type of variable-geometry member for regulating exhaust gas flow through the turbine so as to provide a greater degree of control over the amount of boost provided to the engine by the turbocharger. Such variable-geometry members can include variable vane arrangements, waste gates, sliding pistons, etc.
Linear actuators are frequently employed for providing the motive force to move the variable-geometry member of the turbocharger. An actuator rod or shaft of the actuator is mechanically coupled to the variable-geometry member. Examples of such linear actuators include pneumatic actuators operated by vacuum derived from the engine's intake system.
In order to accurately control the position of the variable-geometry member, typically a sensor assembly is incorporated in the linear actuator for sensing the position of the actuator rod along the nominal displacement path of the actuator rod. One type of sensor assembly comprises a permanent magnet and a Hall effects sensor. The magnet is housed within the movable part of the actuator that imparts movement to the actuator rod. The sensor is disposed in the fixed part of the actuator, proximate the magnet. The nominal displacement path of the actuator rod is usually coincident with the longitudinal axis of the actuator rod. However, often the actual movement of the actuator rod is not a pure translation along the longitudinal axis of the rod, but also includes some amount of rotation of the rod about one or more axes that are not parallel to the longitudinal axis. This complex movement of the actuator rod complicates the accurate sensing of the actuator rod position by the sensor assembly.
Others have tried to address this problem by providing a guiding structure for the actuator rod. The guiding structure surrounds and contacts the actuator rod and constrains it to pivot about a fixed pivot point that is proximate the sensor. The magnet is contained in a part of the rod adjacent the sensor. The objective of this arrangement is to keep the radial spacing between the magnet and the sensor constant regardless of whether the rod is purely translating or undergoing a complex translation and rotation movement.